On a dozen canyon trips over the years, we've had mice issues, but they've never been more of a problem than on any other river. Just have dinner dish crew do a final sweep of the kitchen, and make sure all food makes it back into coolers, ammo cans or dryboxes at night.
The ringtails and ravens were the bigger pests. They're clever! Both can unzip backpacks. At Bass Camp, on broad daylight, the ringtails dragged off my solar charger and camera batteries (we caught up with them partway back to their lair). I've never seen them out during the day! And at Nankoweap, the ravens unzipped my pack and flew some of my clothing into a tree... That was fun.